o much nitrogen, due to heavy manuring or
other cause, produces an excessive growth of stalk or straw, at the
expense of grain production, in the case of corn, wheat, and other
cereals. It produces a rank growth of potato vines and partial failure
of the crop of tubers. It produces a tender growth of straw or vine
that invites injury from fungous diseases. It is the rule that soils
have a deficiency in nitrogen, but when there is an excess, the best
cure comes through use of such crops as timothy, cabbage, and ensilage
corn. Heavy applications of rock-and-potash fertilizers assist in
recovery of right conditions, but are not wholly effective until
exhaustive crops have removed some of the nitrogen.

CHAPTER XXI

TILLAGE

Desirable Physical Condition of the Soil.--Successful cropping of land
is dependent upon favoring soil conditions. The plants to be grown must
have ease in root extension, so that their food may be found. There
must be moisture to hold the food in solution. There must be air. There
must be destruction of plants that would be competitors of the ones
desired. A soil rarely is in prime condition for the planting and
growth of any crop without some change in its structure by means of
tillage, and it does not remain in the best condition for any long
period of time. If the number of plants required per acre for a crop is
relatively small, tillage of the soil is continued after planting. If
the necessary number makes tillage impossible, there is some loss in
conditions most favorable to the plant. The particles of soil settle
together, and there is loss of water at the surface. Most plants want a
mellow soil, and tillage is in large part an effort to make and to keep
the condition of the soil friendly to plant life in this respect. The
wide variation in methods of tillage are due to the great differences
in the texture and structure of soils, and to the habits of plants, and
skill in selection of methods is a measure of the intelligence used in
farming.

The Breaking-plow.--Land containing enough clay to give it an excellent
soil inclines to become firm. During the growth of a crop, when plant
roots fill the soil and prevent deep stirring, the particles pack
closely together, limiting the power of the land to make fertility
available. The presence of organic matter counteracts, in part, this
packing tendency, but there are few soils that remain permanently
mellow. The breaking-plow is used to loo